With the development of optical network communication techniques, the method of using optical fibers to transmit signals has become a mainstream of network traffic transmission. During the transmission process of optical networks, instances affecting traffic transmission, such as a fiber break and a node failure, may possibly take place at any moment. In order to improve the reliability of traffic transmission, and raise the usability of optical networks, protective measures aiming at possible situations which may affect traffic transmission are required in the OTN. The protective measures are generally set as adopting certain backup resources to protect active resources, and when any abnormality arises to the active resources, traffic transmission will be taken over by the backup resources.
At present, a protection scheme of two-fiber MS shared protection ring is adopted in the Synchronous Digital Hierarchy (SDH) field to realize traffic protection. The detailed implementation is adopting two fibers, whose transmission directions are opposite, For N time slots of each fiber of the MS, the former half of the time slots (1 to N/2) in one fiber are regarded as working time slots, and the latter half of the time slots (N/2+1 to N) in the other fiber are regarded as protection time slots of the corresponding working time slots. When a failure such as a fiber breaking occurs, K1 byte and K2 byte are employed to deliver protection switching information between different nodes. Then, bridging and switching are implemented at both end nodes of the broken fiber.
The prior art has the following characteristics:
It is only acceptable for SDH field. Only a latter half of channels in one fiber are allocated as protection channels to protect working channels of a former half of channels in the other fiber. The number of nodes permitted for this kind of protection ring is at most 16. Further, the traffic is bridged at both the end nodes of the failure, which will bring unendurable delay for transoceanic applications.
Similarly, a protection scheme based on bidirectional optical line shared protection ring is adopted in technical field of Wavelength Division Multiplexing (WDM).
Referring to FIG. 1, at least two fibers X and Y are needed between two adjacent nodes in this method. One half of wavelengths in each fiber are set to carry working signal S, and the other half are set to carry protection signal P. That is, the fiber X simultaneously transmits signal of working wavelength S1 in working section W, and signal of protection wavelength P2 in protection section P; the fiber Y simultaneously transmits signal of working wavelength S2 in working section W, and signal of protection wavelength P1 in protection section P. The working wavelength S1 of one fiber is protected by the protection wavelength P1 of the other fiber in opposite direction of the ring, and vice versa. Also, bidirectional transmission of working traffic is permitted in this method.
When the two fibers between node A and node B are cut off, referring to FIG. 2, node A and node B adjacent to the broken point may find the failure via detecting optical powers. Then, node A and node B will locally control optical switching to connect the S1/P2 fiber and the S2/P1 fiber, and thereby transmit signals from the working wavelengths of the S1/P2 fiber and the S2/P1 fiber to the protection wavelengths of the other fiber to complete protection switching.
It could be seen from the above that, path of the optical signal will become longer after switching, and thus circumference of the ring circuit may be limited. Moreover, optical power is used as the switching initiating criteria in this method. so that line performance monitoring is insufficient, i.e., signal quality detection aiming at the optical line may not be fully carried out to determine SF/SD conditions, which lead to the unreliability of protection switching. Therefore, this method only accommodates the WDM field.